In natural marine conditions the buffering action of bicarbonates and carbonates maintains the pH at a very constant value of 8.2 - 8.4. This value should be replicated in your marine aquarium because all forms of life, from fish and plants to algae and filter bacteria can show adverse reactions if kept outside their preferred pH range, or if subject to sudden changes in the pH value. The pH value of water is a measure of the degree of acidity or basicity, with values ranging from 1 (acidic) through 7 (neutral) to 14 (basic). The Tetratest?? pH kit was professionally developed to accurately determine the pH level in your aquarium water. The kit contains one 10-ml test reagent (enough for 50 tests), a test vial, color scale, instructions and recommendations. Test the water in your aquarium weekly to ensure optimum water quality Info from United Pet Group